Novel N-substituted indol-3-ylglyoxylamides probing the LDi and L1L2 lipophilic regions of the benzodiazepine receptor site in search for subtype-selective ligands

Novel N-substituted indol-3-ylglyoxylamides (10-37) were synthesized and evaluated as ligands of the benzodiazepine receptor (BzR). In an effort to achieve affinity-based selectivity among BzR subtypes, these compounds were designed to probe the LDi and L2 lipophilic regions. Taking the α1-selective benzylin-dolylglyoxylamides Ia and Ib as leads, we varied the substituent on the benzylamide phenyl ring (compounds 10-23) or replaced the benzyl moiety with alkyl groups (compounds 24-37). The above structural changes gave no shift of selectivity from the α1 toward the α2 or α5 subtypes, thus confirming that a ligand which occupies the LDi region probably exhibits α1-selectivity, despite its interactions with other lipophilic areas in the receptor binding cleft. Compound 11 (N-(p-methylbenzyl)-5-nitroindol-3-ylglyoxylamide), which selectively binds with a full agonist efficacy at the α1 receptor subtype and displays sedative action, can be regarded as an interesting potential zolpidem-like sedative-hypnotic agent.